The present invention relates to an apparatus for controlling the tilt angle of a doctor blade.
In doctor blade applicators, the amount of coating mix applied to the web is controlled by adjusting the loading of the blade. However, changes in the degree of blade loading also causes a change in the blade's tilt angle, which complicates blade control.
In prior art doctoring units, the blade position has been manually adjusted as required. Compensation systems for blade tilt angle are also known. Finland patent application No. 844035 discloses an apparatus in which two synchronously operated jacks are used to set the degree of blade loading. Finland patent application No. 793164 discloses an apparatus in which loading control is effected by adjusting the shape of the blade while the blade supporting beam is stationary. In this case, the blade supporting beam incorporates a complicated control system for the adjustment of blade stiffness. In a system described in Finland patent application No. 2203/74, loading control is achieved by rotating the blade frame about a shaft, thus causing a deformation of the blade shape and simultaneously altering the reaction force of the blade, while maintaining a constant blade tilt angle.
Manual blade control by methods of conventional technology is slow and incapable of complying with all loading conditions, which results in undesired deviations in the amount of coating mix applied. Compensation systems for doctor blade tilt angle deviations known in the art are complicated in structure, high in cost, and prone to malfunction.
The aim of the present invention is to overcome the disadvantages associated with the aforedescribed prior art technology and achieve a totally new kind of apparatus for controlling the tilt angle of a doctor blade.
The present invention is based on a structure, where a rotatable support beam is supported by a guiding cam against a blade load adjusting device so that the rotation of the beam moves the beam closer to the web, thus increasing the blade loading, while the angle included by the blade tip and a tangent drawn to the contacting point of the tip is maintained constant or controlled in a desired manner.
The blade tilt angle controlling apparatus achieves, by means of an apparent adjustment of the tilt angle, a change in the blade loading while the actual tip angle remains constant, thus simplifying the adjustment of the coating mix application. Thus, the invention provides outstanding benefits.